In the past, I've upgraded Ubuntu 10.10 to Ubuntu 11.04 using the auto-upgrade function. Unfortunately, the upgrade didn't go very well, and I ended up with a broken 11.04. Because of that, I had to manually reinstall 11.04 from a LiveUSB.
After that, I didn't want to risk to get my system broken again, so six months after, I installed 11.10 from a LiveUSB too, instead of upgrading from 11.04.
But this method starts to annoy me, and I'd like to use the auto-upgrade function to upgrade from 11.10 to 12.04 in April. Besides of making a full-system backup, what can I do to make this Ubuntu upgrade go as smoothly and error-free as possible?